Ultrafast Nonlinear Optical Absorption And Refraction Dynamics Of 6H-SiC Crystal

As one of the third generation semiconductor materials, 6H-SiC has a broad application in the fields of electricity and optics due to its wide band gap, excellent thermal conductivity, mechanical properties, as well as high electron density and charge mobility. In this paper, we investigate the ultrafast nonlinear absorptive and refractive dynamics of 6H-SiC as followed:1) The sign and magnitude of SiC’s third-order optical nonlinearity was determined by Z-scan technique. The results showed reverse staurable absorption and positive nonlinear refraction under 515 nm and 800 nm wavelength. Comparing to the theoretical model, the reverse saturable absorption was assigned to two-photon absorption and the positive nonlinear refraction was originated from Kerr effect. Horizontal comparison of N-doped and undoped 6H-SiC indicated that N doping enhanced both the nonlinear absorption and refraction of 6H-SiC. Based on the results of 515 nm and 800 nm, the influences of indirect and direct transition was investigated.2) The ultrafast absorption and refractive kinetic processes of N-doped 6HSiC and 6H-SiC were studied via femtosecond phase pump-probe. Transient two-photon absorption and positive Kerr effect was observed at zero time, which was agreed with Z-scan data. The influence of doping on carries relaxing was investigated.3) Femtosecond transient absorptive spectra was employed to study the kinetics of carrier absorptive spectra of 6H-SiC. The changing of transient absorptive spectra induced by N-doping was discussed. Results showed the excrescence of doping energy state could enhance transient carrier absorption in specific optical wavelength.